Prostate cancer aetiology : epidemiological studies of the IGF- and one-carbon metabolism pathways

Sammanfattning: The aim of this thesis was to investigate the involvement of the insulin-like growth factor- and the one-carbon metabolism pathways in prostate cancer aetiology, studying both circulating biomarkers and genetic variation. Papers included in the thesis were conducted within the case-control study CAncer Prostate in Sweden (CAPS), and the two prospective studies European Prospective Investigation into nutrition and Cancer (EPIC), and Northern Sweden Health and Disease Cohort (NSHDC).In paper I, we investigated the relation between genetic variants of the IGF1 gene and prostate cancer risk within the CAPS study. We found that a common haplotype within the 3’ region of the IGF1 gene is associated with increased prostate cancer risk.In paper II, we investigated if the variants of the IGF1 gene that were associated with prostate cancer risk in paper I, are also associated with circulating levels of IGF1. Circulating levels of IGF1 were analysed in controls from the CAPS study and three haplotype tagging SNPs (htSNPs) were genotyped in subjects from the NSHDC study in which circulating IGF1 had previously been analysed. The genetic variants previously associated with increased prostate cancer risk were now also found to be associated with elevated levels of circulating IGF1. We concluded that variation in the 3’ region of the IGF1 gene affects prostate cancer risk by influencing circulating levels of IGF1.In paper III, we investigated if variants of the IGFBP1, IGFBP3 and IGFALS genes are associated with i) prostate cancer risk, ii) circulating concentrations of total and intact IGFBP3, and iii) prostate cancer-specific survival probability. In addition, we investigated if circulating concentrations of total and intact IGFBP3 are associated with prostate cancer-specific survival probability. No association between genetic variation and overall prostate cancer risk or survival was observed, but we found a strong association between elevated levels of intact IGFBP3 and increased risk of prostate cancer-specific death. We could, however, not exclude that this association was confounded by treatment or by the tumour.In paper IV, we investigated if circulating levels of folate and vitamin B12 are associated with prostate cancer risk within the EPIC study. We observed no associations between levels of folate, vitamin B12 and overall prostate cancer risk, but elevated levels of vitamin B12 were associated with increased risk of advanced stage disease.In paper V, we investigated if circulating levels of ten B-vitamins and related metabolites within the one-carbon metabolism pathway are associated with prostate cancer risk within the NSHDC study. Overall positive associations with prostate cancer risk were observed for levels of choline, vitamin B2 and vitamin B12, and inverse associations were observed for levels of homocysteine and MMA. We also observed a biologically plausible risk modification by smoking status on the association between vitamin B12 and risk; in non-smokers vitamin B12 was positively associated with risk, whereas the association between vitamin B12 and risk was inverse or null in ever/current-smokers.In summary, our results suggest that genetic variation of the IGF1 gene affects prostate cancer risk by affecting circulating levels of IGF1. The association between circulating concentrations of intact IGFBP3 and prostate cancer-specific survival is intriguing, but further studies are needed to conclude if this association is caused by confounding. We also observed associations between several factors of one-carbon metabolism and risk, but these associations were statistically week and require confirmation in other prospective studies.